Nonhuman primates can easily escape from any ground-dwelling predator by handily scampering up a tree trunk. Evolution redesigned the bipedal foot for walking on flat surfaces. During its extensive overhaul, the human foot relinquished the flexibility and grasping power typical of every other primate. In a climbing contest among all the species of primates, Homo sapiens would come in dead last.
Men can shinny up trees better than women. Their greater upper-body strength somewhat compensates for their feet’s inferior tenacity. A man, much less a woman with small children, cannot outrun any major mammalian or reptilian land predator. Menses and bipedalism would have been a dangerous combination in the forest primeval and an often fatal one out on the nearly featureless savanna. A menstruating woman’s leakage of even the most minute amount of blood would lay down a convenient trail of spoor that a predator could easily track, leading it to both her and her young.*
Some scientists have argued that the previous discussion is not pertinent, because predators instinctually do not like to dine on human flesh: It is not particularly flavorful. The significant number of humans attacked and eaten by bears, tigers, lions, and crocodiles in historical times invalidates this argument. The more likely reason that predators shy away from humans is that they have acquired an instinct ethologists call “flight distance.” Humans have become so dangerous to other animals, including predators, that only those that have learned to avoid us have survived. But at the outset of our species, when the changes I speculate took place, predators would not yet have been so cautious.
The radical hormonal flip-flop that initiates human menses creates conditions within the breasts, ovaries, and uterus that over time predispose the cells making up their linings to cancer. No other species’ females in the wild experience high cancer rates in their reproductive organs, yet these malignancies rank among the leading causes of death for young women today.* There is little reason to doubt that ancestral women did not experience relatively high cancer rates in their reproductive organs. Admittedly, most did not live long enough to be affected, but the loss of even one old wise woman in a tribe to a reproductive organ’s cancer could have seriously diminished a group’s chances for survival.
Jared Diamond recounts his experience working with isolated South Pacific islanders.
When I began pestering my middle-aged Rennellese informants with my questions about fruit edibility, I was brought into a hut. There, in the back of the hut, once my eyes had become accustomed to the dim light, was the inevitable, frail, very old woman, unable to walk without support. She was the last living person with direct experience of the plants found safe and nutritious to eat after the hungi kengi [cyclone], until people’s gardens began producing again. The old woman explained to me that she had been a child not quite of marriageable age at the time of the hungi kengi. Since my visit to Rennell was in 1976, and since the cyclone had struck sixty-six years before, around 1910, the woman was probably in her early eighties. Her survival after the 1910 cyclone had depended on information remembered by aged survivors of the last big cyclone before the hungi kengi. Now the ability of her people to survive another cyclone would depend on her own memories, which fortunately were very detailed.5
Had this one particular woman died of a reproductive cancer earlier in life, the consequences for the entire tribe would have been calamitous.
Another deleterious effect of menses concerns Free Will. Humans are extremely proud of their unique ability to override their instincts, drives, and hormones and rise above the urgent demands of thirst, hunger, sleep, fatigue, and sex. We can voluntarily forgo eating even to the point of starvation. We enter convents and monasteries pledging to live a celibate life. We can work hours without sleep. We can control (up to a point) our bladder and bowels. Yogi adepts can regulate their heart rate and breathing to a remarkable degree. We admire heroes and heroines who control their destinies through their forceful characters, delaying gratification to achieve majestic goals. We marvel at the discipline and willpower necessary to become a virtuoso pianist, an Olympic gold medalist, or a Nobel Prize winner.
We are exceptionally proud that we can rein in the part of us that we consider our “creatureliness.” However, one bodily function resisting volitional control, except under the most extreme circumstances, is the timing of a woman’s menstrual cycle.* It is for naught that a woman brings to bear mental fortitude and concentration determined to change the appointed day.
Her inevitable resignation to the power her monthly cycle exerts upon her will contributes, I believe, to a woman’s receptivity to accept “fate,” a passive mental attitude more commonly associated with the feminine than the masculine. Whether this is a disadvantage or an advantage is debatable, but a man’s greater reluctance to accept matters as they stand is, in no small part, due to the fact that he does not experience a monthly bodily function, comparable to menses, over which he cannot impose his will.†
One of the most detrimental side effects of human menses is the prevalence of the gynecological condition of endometriosis. This distressing disease plays virtually no role in the well-being of any other species’ females. One in ten women of reproductive age in the industrialized nations suffers from it, and it at present constitutes the most common cause of female admissions to hospitals.7 The volume of blood and tissue lost during each human menstrual cycle surpasses that of any other animal. The uterine contractions required to expel it are, therefore, proportionately more energetic. In some cases, their propulsive intensity nearly equals the force of uterine contractions delivering a full-term fetus.8 These monthly spasms can cause uterine tissue to relocate to other areas within the woman’s abdominal cavity.
When a woman’s period begins, her menstrual contents must exit via the narrow tunnel in the cervix, the tubular outlet of the uterus that leads into the upper vault of the vagina. During menses, the opening in the cervix enlarges to accommodate this exodus. In some women, however, not all of the compressed blood and tissue can escape through this preferred channel; some of it is forced to exit through two alternative openings into the uterine cavity, the entrances of the horn-shaped fallopian tubes, high on either side of the uterine apex.
Normally, the fallopian tubes function as follows. At midcycle, the ovary releases an egg into the interior of the peritoneal cavity. Nearby, beckoning the ovum on the fallopian tube’s trumpet-shaped extremity is a delicate circular fringe resembling the fingers of a sea anemone. These waving, frondlike fimbriae gently scoop up the egg and funnel it into the tapered portion of the fallopian tube’s narrow passageway. Through gentle, undulating waves, the ovum is then milked slowly toward the womb’s great chamber. The fallopian tube’s design allows peristaltic movement only in a wombward direction.
A schematic of the human female reproductive pelvic organs.
The force of the human uterine contraction during menses, however, can cram a small amount of menstrual blood and cellular debris along the length of the pencil-sized fallopian tubes. Overpowering the fallopian muscular contractions, uterine contractions can occasionally propel menstrual contents to the tube’s fimbrial opening, spilling some of the waste products out into the peritoneal cavity.
The specialized sentinel cells making up the pelvic peritoneal lining react vigorously to the foreign material invading their pristine landscape. An aroused peritoneum responds, activating pain reflexes, and the bedeviled woman experiences abdominal discomfort different from that associated with normal menstrual cramps. Locally, the peritoneal membrane mounts an inflammatory counterattack. White blood cells, the immune system’s military arm, rush to the scene and, along with other reinforcements, slay, disrupt, and absorb what is left of the foreign invaders. When the conflict is over, the peritoneal lining resembles a scarred and roughened battlefield. Adhesions composed primarily of collagen, the body’s first phase in trying to heal the area, appear. The blood vessels supporting their enterprise permanently enlarge.
On occasion, some of the cells belongi
ng to the uterine lining that were near death manage to escape the detection of the vigilant white-cell patrols, and they possess sufficient vitality to latch on to a contiguous organ or transplant onto the newly perfused peritoneal lining. Like a weed blown into a fertile garden, these errant uterine cells take hold, insinuating themselves in their new hospitable surroundings. Patches of uterine lining begin to sprout where no uterine lining was ever intended. Bowel, bladder, ovary, and the outer surface of the uterus all become potential hosting sites. The displaced cells then transform into true parasites, drawing all their nutrition and oxygen from the reluctant hosts. The cruelty of their incursion soon becomes apparent. The doleful symptoms of endometriosis now unfold.
Uterine-lining cells are very responsive to a woman’s reproductive cycle’s hormones circulating throughout her entire body. Molecules of estrogen and progesterone cannot distinguish whether their target cells are in the uterus or growing on the peritoneum. Displaced endometrial tissue increasingly swells and grows turgid with blood in the days following midcycle, exactly mimicking the response of cells inside the uterus. At the end of a cycle, the diaspora cells suffer the same fate as intrauterine cells if conception does not occur—they die. But endometrial carpetbaggers have nowhere to go and must die in place. There is no mechanism by which the body can rid itself of this small but significant toxic load.
Endometrial cells’ necrotic implosion initiates another cycle of peritonitis, inflammation, scarring, and adhesions. A woman afflicted with endometriosis will experience periodic pelvic pain and, on occasion, severe discomfort during the sexual act, called dyspareunia. Infertility is another baleful consequence.
There is no reason to believe that ancestral women had weaker uterine contractions or a lesser volume of menstrual effluvia requiring expulsion. I conjecture that they, too, suffered from endometriosis.* Ancestral women, however (because of their more frequent pregnancies and lactation), experienced relatively fewer cases of endometriosis than contemporary women. But the few debilitated women suffering from this condition constitute another dramatic reason why heavy menses would have been an undesirable addition to Gyna sapiens’ life story.
If a wounded animal bleeds excessively, a hunter anticipates that it will soon collapse. Animals that bleed intuit instinctively that they have been injured, and will retreat to the back of the cave or burrow to lick their wounds. A predatory hominid male would be acutely aware that copious bleeding in a wounded animal is an event preceding its death.
Imagine, then, the awe, fright, and confusion that men experienced when they furtively caught sight of a woman’s menses. Women bled, but they did not grow weak. They bled, but they were not injured. They bled, but they did not die. Sexual relations with a menstruating female would conclude with the male’s withdrawing a blood-smeared member. Feeding many males’ innate castration fears, this disturbing sight would tend to cool a man’s ardor and make him believe that a menstruating woman possessed a power beyond his ken. Menses would seem to him to be some sort of magic. Perceived supernatural powers induce fear, and men began to fear women. This in turn led men to resent women, because, even though they were bigger and stronger, men were afraid of the otherworldly supremacy they imputed to women.
The sheer inconvenience of monthly bleeding also creates hygienic problems, especially to ground-dwelling nomadic females. Keeping clean while on the move, at present problematic for women living in developing nations, would have been extremely difficult in the Pleistocene. Fabrics were nonexistent, large hides were not yet plentiful, and appropriate plant substitutes were not always readily available. Remaining at a home base instead of traveling daily presented a menstruating woman with a different set of problems. Special handling of menstrual effluvia became imperative. Dependent on the purity of local water supplies for drinking, washing, and bathing, men and women would have had to address the issue of menses communally.
Extrapolating from what anthropologists have gleaned from male attitudes toward menses in extant hunter-gatherer cultures, early Homo sapiens would most likely have insisted on measures to isolate the menstruating women in the group as he became increasingly aware of Gyna sapiens’ menses. Fastidious women would have already disengaged from the others during their monthly times and sought out other women similarly indisposed. Perhaps men and women voluntarily supported these restrictions for the good of the tribe. Later, these strictures, passed down through generations by ritual and tradition, became menstruation taboos, the vast majority of which, over time, have served to strip political power and autonomy from women.
Among the Bribri Indians of Costa Rica, a menstruating woman was considered unclean. She was forbidden to come near a male’s hunting weapons or touch any food or utensils. The only plates she could use for her food were banana leaves, which she had to abandon in a sequestered spot because it was believed that if a cow ate them the animal would die.9 In the Jewish Orthodox tradition, the period of niddah circumscribes five days of menstruation followed by seven days free of discharge. During this period, a woman is considered “impure.” According to one rabbi’s interpretation of the niddah laws, “One should therefore be careful that the beds are far enough apart to ensure husband and wife will not touch each other when they sleep. He may not sit on her bed even when she is not present. He is forbidden to take care of her when she is ill unless there is no one else, and she is in great need of it.”10 The first-century-A.D. Roman pseudo-scientist Pliny warns men that a menstruating woman, by her touch, can “blast the fruits of the field, sour wine, cloud mirrors, rust iron, and blunt the edges of knives.”11 During the witch craze that convulsed Renaissance Europe, accused women purportedly had the magical powers to do the very things that Pliny’s menstrual superstitions attributed to a woman having her period.
Initially, elders may have instituted menstrual restrictions for rational hygienic reasons. Menstrual blood is a rich medium, encouraging the growth of pathogenic organisms. Its proper disposal had to be regulated. Predators had to be kept at bay. Prey must not be alerted to the presence of hunters by whiffing the scent of a menstruating female who might be among them. When dealing with something as mysterious as menses, however, the irrational quickly trumped the rational. Men put women in an untenable position by insisting that it was their responsibility to assuage men’s menstrual fears. The powerful taboos associated with menses among indigenous peoples, as well as many that persist in modern cultures, are testament to the tenacity of these beliefs—which, in many cases, are nothing more than misguided superstitions.
Anthropologist Camilla Power put forth the idea that menstruation was beneficial to the human species because it provided men with the only reliable clue that they could use to calculate whether a woman was imminently fertile. In a population of women who were either pregnant or lactating, the occasional menses would be an important signal. “Pleistocene males who were attentive to recently menstruating females in an effort to increase their mating prospects,” Power wrote, “should therefore enhance their fitness. No male could afford to ignore this signal.”12 According to Power, menstrual rituals evolved to become complex coalitionary attempts by all the tribe’s women to confuse the men as to the timing of a woman’s menses, which in turn would strengthen the power of women’s veto over sex. In every other species, the female signals the male she is potentially fertile by advertising her ovulation as estrus, heat, rutting season, or any of the many other terms used to describe a female animal’s heightened sexual receptivity. Power’s explanation of why Mother Nature went to the trouble of saddling human females with concealed ovulation and then undid Her efforts by further burdening women with a dangerous blood loss for the purpose of alerting men that pregnancy was a possibility is ingenious but, in my opinion, too complex.
Not all women experience menses as a “curse.” Some premenstrual women report an upsurge in positive feelings. Paula Nicholson, after reviewing interviews with many women, reported, “The premenstrual phase of the cycle is frequentl
y accompanied by heightened activity, intellectual clarity, feelings of well being, happiness, and sexual desire.”13
And not all the taboos and rituals associated with menses detracted from a woman’s well-being. Some women would have welcomed these restrictions, which afforded them an opportunity to create zones that men dared not trespass. Camaraderie and freedom from the daily grind allowed congregating women to create, tell stories, and rest. In the apocryphal Red Tent, women could pass along valuable lore and woman wisdom from one generation to another. But these are, remember, cultural advantages that occurred long after the human line developed sophisticated cultures. The original question I posed was: What evolutionary advantage did menses provide to advance the fortunes of individual females of the human species? Why did it evolve in the first place?
Hippocrates, the classical-Greek father of medicine, believed that menses flushed “poisonous” humors monthly from a woman’s body, a necessary cleansing, he was sure, that prevented the accumulation of toxins. Menses supposedly promoted a woman’s health. Galen, the influential second-century Roman physician, endorsed Hippocrates’ theory, and this unsubstantiated belief has persisted in one variation or another right up to the present day.*
Margie Profet, an evolutionary biologist, proposed in 1993 that menses purges the uterus of possible microscopic pathogens that may have hitchhiked on the sperm of the previous month’s suitors.14 Profet arrived at her controversial conclusion because she was convinced that something as detrimental as menses must have a benefit to the species—otherwise it would have been culled from the genome long ago.
Skin is an impermeable membrane that covers and protects the body. When skin becomes denuded, as happens in the case of a third-degree burn or a scraping injury from trauma, the raw tissue beneath becomes exposed. Raw surfaces stripped of their protective lining and then coated with blood provide the ideal conditions for the overgrowth of pathogenic bacteria. If the surface is an internal one kept at an optimal incubating temperature of 98.6°F, the bacteria will multiply even faster.
Sex, Time, and Power Page 9
